Varactor loaded tunable split ring resonators with simple biasing network

A concept for a voltage tunable split ring resonator array inside a WR90 waveguide operated below its cutoff frequency is presented. The DC tuning voltage is provided by using the existing RF structure for DC biasing. Tuning the semiconductor varactors shifts the backward wave transmission band below the waveguide cutoff frequency in the range of 0.9-2.2 GHz. The parasitic effects of the biasing network as well as the higher order mode coupling in the macroscopic structure are investigated. Experimental results are compared to theory in order to validate the biasing concept.